1. Field of the Invention
The present invention relates to a Cu-based sintered alloy bearing which exhibits excellent wear resistance when applied to small motor fuel pumps driven at high rotation speeds.
2. Background Art
Generally, an engine that uses, as a fuel, liquid fuel such as gasoline or light oil, has conventionally been equipped with a motor fuel pump. As the motor fuel pump for a gasoline engine, for example, a motor fuel pump shown in FIG. 1 is known.
In the motor fuel pump shown in FIG. 1, a rotating shaft 3 fixed to both ends of a motor 2 is supported by a bearing 4 in a casing 1. Into one end of the rotating shaft 3, an impeller 5 is inserted and also a narrow gasoline passage is formed along the outer periphery of impeller 5, the outer periphery of the motor 2 (armature) and the space (not shown) between the bearing 4 and the rotating shaft 3. The reference symbol 6 denotes a magnet.
The bearing 4 is made of various Cu-based sintered alloys.
When the motor 2 is rotated to rotate the impeller 5, gasoline is charged into the casing 1 as a result of the rotation of the impeller 5. The charged gasoline is sent to a gasoline engine provided separately through the outer peripheral surface of impeller 5, the outer peripheral surface of the motor 2 (armature) and the space (not shown) between the bearing 4 and the rotating shaft 3.
In the pump shown in FIG. 1, an extremely small quantity of gasoline, the pressure of which was raised by the impeller 5, pass through the outer peripheral portions of both being 4 and, furthermore, gasoline reaches the outer peripheral surface of the armature through a fuel passage (not shown) of the casing.
With recent remarkable development of light-weight and high-performance engines for automobiles, size reduction of fuel pumps used in the engines has been strongly required. In the case of the motor fuel pump having the above structure, high drive that is, an increase in rotation speed, is required to yield size reduction while maintaining discharging performance.
Since liquid fuels such as gasoline charged into the fuel pump flows through a narrower passage at a high flow rate under high pressure, higher strength and excellent wear resistance are particularly required of a bearing of a motor fuel pump.
However, no conventional Cu-based sintered alloy bearing has sufficient strength or sufficient wear resistance and therefore wear progresses rapidly. Furthermore, in the case in which liquid fuel contains sulfur or a compound thereof as impurities, wear is further accelerated, resulting in failure within a relatively short period.
Under these circumstances, the present inventors have studied to develop a bearing suited for use in a small motor fuel pump driven at high rotation speed.
As a result, they have found that the following effects (1) to (3) can be obtained in the following three kinds of aspects (A) to (C):
(A) a bearing for a motor fuel pump is made of a graphite dispersion type Cu-based sintered alloy with a composition consisting essentially, by weight (hereinafter, percentages are by weight unless otherwise stated), of 20 to 40% of Ni, 0.1 to 0.9% of P and 1 to 8% of C, and the balance of Cu and inevitable impurities, the Cu-based sintered alloy having, a porosity of 5 to 25%;
(B) a bearing for motor fuel pump is made of a Cu-based sintered alloy with a composition consisting essentially of 20 to 40% of Ni, 0.1 to 0.9% of P and 0.5 to 5% of molybdenum disulfide (hereinafter referred to as MoS2), and the balance of Cu and inevitable impurities. This alloy has a structure wherein a hard Cu-P compound and molybdenum disulfide having high lubricity are dispersed and distributed in a matrix made of a solid solution phase of a Cuxe2x80x94Ni alloy, and has a porosity of 5 to 25%; and
(C) a bearing for motor fuel pump is made of a Cu-based sintered alloy with a composition consisting essentially of 20 to 40% of Ni, 0.1 to 0.9% of P, 0.5 to 5% of C and 0.5 to 5% of MoS2, and the balance of Cu and inevitable impurities. This alloy has a structure wherein a hard Cuxe2x80x94P compound as well as free graphite and molybdenum disulfide having high lubricity are dispersed and distributed in a matrix made of a solid solution phase of a Cuxe2x80x94Ni alloy, and has a porosity of 5 to 25%.
The effects obtained by the above respective aspects (A) to (C) are as follows.
(1) Through pores in the bearing, liquid fuel is supplied to the inner peripheral surface of the bearing from the outer peripheral surface of the bearing, and thus a fluid lubricating film is formed and frictional resistance of the bearing caused by high-speed rotation of the motor is relieved by an action of the fluid lubricating film.
(2) Although the wear resistance is lowered in proportion as pores are formed, the hard Cuxe2x80x94P compound dispersed and distributed in the matrix made of the solid solution phase of the Cuxe2x80x94Ni alloy as well as free graphite having high lubricity and/or high-lubricating molybdenum disulfide MoS2, which are also dispersed and distributed in the matrix, make up for lowering of the wear resistance. Therefore, the bearing exhibits excellent wear resistance in environments exposed to liquid fuel flowing through at high flow rate under high pressure by the synergistic effect of high strength and excellent corrosion resistance of the Cuxe2x80x94Ni alloy constituting the matrix.
(3) Also these Cu-based sintered alloy bearings exhibit excellent corrosion resistance to liquid fuel containing sulfur or a compound thereof as impurities.